What is not common knowledge, they write, is “that the Social Security Administration underestimates how long Americans will live and how much the trust funds will need to pay out—to the tune of $800 billion by 2031, more than the current annual defense budget—and that the trust funds will run out, if nothing is done, two years earlier than the government has predicted.”

The authors offer two suggestions for saving Social Security: One is to keep raising the age at which people become eligible for full retirement.